Great Nephew Day has arrived, and Fry gets the Professor a present in the form of a glowing green rock that is legally distinct from Kryptonite on by the fact that it's not called by the same name. Also, its effects on Superman are unknown. Its effects on Fry and the Professor, if they both wear it simultaneously around their necks, is that once they both sleep, they will awaken with the other's body. The only thing is, the Professor wants to keep it a secret for a while so that he can use Fry's body to be young again, while Fry is just presumed to be the Professor acting insane and he's taken away.[1]